Resin-forming material, implant material and compositions for restorative material suitable for medical or dental use

ABSTRACT

Resin-forming material suitable for medical or dental use comprising tetramethylolmethane tri- or tetracrylate or tetramethylolmethane tri- or tetramethacrylate; and implant material suitable for medical or dental use comprising nitride of at least one member of metal selected from the group consisting of Group IVB, Group VB and Group VIB in the periodic table of elements and boron, aluminum and silicon and having Mohs&#39; scale of hardness of at least 7.

This is a continuation of application Ser. No. 138,814, filed Apr. 9,1980, now U.S. Pat. No. 4,327,014.

The present invention relates to resin-forming material suitable formedical or dental use, and more particularly, to resin-forming materialapplicable in the field of repairing bones and teeth which is extremelyexcellent in physical properties, such as hardness, compressivestrength, abrasion resistance and so on, as well as in bonding to thehard tissue of the human body.

The present invention further relates to a restorative implant materialsuitable for medical or dental use, and more particularly, to theherinafter-described restorative implant material for the human bodycomprising specified metal nitride.

Moreover, the present invention relates to restorative material suitablefor medical or dental use consisting predominantly of said resin-formingmaterial suitable for medical or dental use and said restorative implantmaterial.

First, explanations will be given below about the resin-forming materialsuitable for medical or dental use according to the present invention.

Among the materials for medical or dental use, particularly dental use,the dental amalgam consisting of silver alloy and mercury, and silicatecement have hitherto been used as restorative filling materials. Theamalgam, however, shows a low degree of seal to the margins of a toothcavity because of its inferior impact strength in addition to itsinferior bonding property to teeth, and also there is the feat that itwill exert an unfavourable influence on the human body because oftoxicity. Further, the silicate cement is readily soluble and entailssuch shortcomings as pulpal irritation in addition to a low degree ofbonding property to teeth and an inferior marginal seal.

Whereupon, for anterior teeth, developments have been made of a materialconsisting predominantly of bisphenol A diglycidyl methacrylate(hereinafter called "Bis-GMA" for short) and an inorganic filler, suchas α-quartz (hereinafter called the Bis-GMA type composite resin), as anew restorative filling material useful as a substitute for conventionalsilicate cement (refer, for instance, to the U.S. Pat. Nos. 3,539,533;3,066,112; 3,926,906, etc.). This material has improved properties suchas compressive strength, water resistance, pulpal irritation and so onas compared to conventional materials, such as said silicate cement, andit is widely used. But that material is still far from satisfactory inthe aspects of physical properties, such as hardness, compressivestrength, abrasion resistance and so on, or bonding to teeth and thelike. In the case of Bis-GMA, it is not completely satisfactory even foranterior teeth, not to mention that it is next to impossible to apply itto molars which are subjected to higher occlusal pressures than anteriorteeth.

With the Bis-GMA type composite resin, as the reason why said physicalfunctions are not sufficient, it can be said that Bis-GMA isinsufficient in physical properties as a resin, becuse it is low incross-linking and it has a high viscosity. Even if diluents were jointlyused therewith, the amount of the inorganic filler which is jointly usedfor the purpose of improving the physical properties of restorativefilling material is restricted.

As a reson why the Bis-GMA type composite resin is poor in the bondingproperty to teeth, it can be mentioned that because of the joint use ofa great deal of inorganic filler, in addition to the somewhat poorbondability to teeth of Bis-GMA, the viscosity of the composite resin isincreased, resulting in a poor wettability on the tooth surface.

In order to improve the various shortcomings of the Bis-GMA typecomposite resin, attempts were made to increase the cross-linking of theresin and increase the amount of inorganic filler used therewith byusing such low viscosity multifunctional monomers as trimethylolpropanetrimethacrylate (hereinafter called "TMPT" for short) instead of Bis-GMAas disclosed in British Pat. No. 1,451,262, for instance. But in thecase of TMPT, bonding to teeth is hardly shown because it has no polargroups and the viscosity of TMPT is too low, which gives rise to suchproblems as a lack in the surface curability of the composite resin andsettling of the inorganic filler in paste condition.

In the case, further, of TMPT, pulpal irritation caused by the residualmonomer is very severe.

The instant inventors studied for the purpose of solving said variousdrawbacks with conventional dental materials, in consequence of which itwas found that by using a resin-forming material consistingpredominantly of the hereinafter-described acrylic monomer of thespecified structure, there could be obtained a material for medical ordental use which is excellent in various physical properties, such ashardness, compressive strength, abrasion resistance and so on, weak intissue irritation and in addition, excellent in bonding to the hardtissue of the human body.

The present invention is designed to provide a resin-forming materialsuitable for medical or dental use which is excellent in variousphysical properties, such as hardness, compressive strength, abrasionresistance and so on, weak in the tissue irritation and added to this,extremely good in the bonding to the hard tissue of the human body.

Another purpose of the present invention in to provide resin-formingmaterial suitable for medical or dental use which is excellent invarious physical properties, tissue irritation and bonding to the hardtissue and good in operation in its practical use.

The other purposes and merits of the said resin-forming material of thepresent invention will be clear from the explanations which follow.

According to the present invention, the said purposes and merits couldbe achieved by a resin-forming material suitable for medical or dentaluse comprising at least one member of compounds represented by thefollowing formula (I): ##STR1## wherein Z stands for a hydrogen atom ora group represented by the following formula ##STR2## and R₁, R₂, R₃ andR₄ may be each identical or different and stand for a hydrogen atom,methyl group, ethyl group or n- or iso-propyl group.

Compounds represented by the said formula (I) divide broadly into twoclasses, one is compounds represented by the following formula (II) andthe other is compounds represented by the following formula (III).

Formula (II): ##STR3## wherein R₁, R₂ and R₃ are as defined in theformula (I). Formula (III): ##STR4## wherein R₁, R₂, R₃ and R₄ are asdefined in the formula (I).

According to the present invention at least one member of compoundsrepresented by the formula (II) or (III) can be used as a resin-formingmaterial suitable for medical or dental use.

In the present invention it is preferred to use, as the medical ordental resin-forming material, compositions comprising

(1) 30-100% by weight of at least one member of compounds represented bythe following formula (II). ##STR5## wherein R₁, R₂ and R₃ are asdefined in the formula (I) and

(2) 0-70% by weight of at least one member of compounds represented bythe following formula (III): ##STR6## wherein R₁, R₂, R₃ and R₄ are asdefined in the formula (I).

With the resin-forming material of the present invention the compoundrepresented by the formula (II) should advantageously be mixed inproportions of preferably 30-95% by weight, more preferably 40-80% byweight and most preferably 45-70% by weight and the compound representedby the formula (III) in proportions of preferably 5-70% by weight, morepreferably 20-60% by weight and most preferably 30-55% by weight. If thecompound represented by the formula (II) is less than 30% by weight,viz., the compound represented by the formula (III) is in excess of 70%by weight, in the case, in particular, of using same as a dental fillingmaterial or restorative for a crown bridge, it tends to deteriorate inthe bonding to teeth and operation.

In the instant invention, the said formulae (I), (II) and (III) whereinR₁, R₂, R₃ and R₄ are hydrogen or methyl, in particular, are preferred.In this case, most typically the respective R₁, R₂ and R₃ in the formula(II) or the respective R₁, R₂, R₃ and R₄ in the formula (III) representhydrogen or methyl. Not only that, but also those in which part of R₁,R₂, R₃ and R₄ represents hydrogen, whereas another part of themrepresents methyl, viz., mixed esters of acrylic acid and methacrylicacid, are also preferred.

As typical examples of compounds represented by the formula (II) thereare cited tetramethylolmethane triacrylate and tetramethylolmethanetrimethacrylate, for instance. As typical examples of compoundsrepresented by the formula (III) there are cited tetramethylolmethanetetraacrylate and tetramethylolmethane tetramethacrylate, for instance.

Conventionally, as already mentioned, it is known to use triacrylate ortrimethacrylate esters of trimethylolpropane, but the compound of thesaid formula (II) used in the present invention is characterized bypossessing another methylol group (--CH₂ OH) compared to thosetriacrylate or trimethacrylate esters, and the compound of the saidformula (III) is characterized in that it is a tetrafunctional acrylateor methacrylate ester.

The compound of the said formula (II) is excellent in bonding to thehard tissue of the human body caused by the effect of the four methylolgroups and by using such compound of the formula (II) and compound ofthe formula (III) in combination. In particular, a resin for medical ordental use can be advantageously formed which is excellent in bonding tothe hard tissue of the human body as well as in the compressivestrength.

In the case, further, of using a combination of the compound of formula(II) and the compound of formula (III), the composite resin formedtherefrom is extremely excellent in water resistance besides theaforementioned characteristics and shows very excellent operation on theoccasion of its practical use.

On top of that, the compounds of the present invention represented bythe formulae (II) and (III) can be used in combination with otherpolymerizable monomers, such as conventionally known resin-formingmonomers for medical or dental use. In this case, the amount in whichthe other monomers are incorporated should preferably be set at 40% byweight or less, more preferably 30% by weight or less and mostpreferably 20% by weight or less. In the case where monomers other thanthose of formulae (II) and (III) are contained in as great an amount asto exceed 50% by weight, there is the fear of causing the lowering ofthe various excellent characteristics of the resin composition of thepresent invention and it is not preferred. In this connection, astypical examples of the polymerizable monomers referred to here, therecan be cited bismethacryloxyethoxydiphenylpropane, Bis-GMA, bisphenol Adimethacrylate, neopentylglycol dimethacrylate and so forth.

The resin-forming material of the present invention, in its practicaluse, should usually be used as a composition in admixture with acatalyst for causing the polymerization of the compound of the formula(II) and/or compound of the formula (III) and an activator foraccelerating the formation of free radicals by the reaction with such acatalyst.

Furthermore, the compounds of the formula (II) and/or formula (III) canbe used in combination with any inorganic fillers for medical or dentaluse which are non-noxious to the human body and have a great hardness,such as powdered quartz, powdered glass, glass beads, powdered aluminumoxide, borosilicate glass, barium glass, hydroxy apatite and aluminosilicate, in addition to the catalyst and activator. These inorganicfillers, although it differs according to use, should preferably have aMohs' scale of hardness of at least 5 and, preferably, at least 6. Inthis case, however, the physical properties, as a material for medicalor dental use, are much better if the resin-forming material is used incombination with the hereinafter-described specified metal nitridediscovered anew by the instant inventors. The said inorganic fillershould preferably account for 50-95% by weight, preferably 50-90% byweight, and most preferably 70-90% by weight, based on the total amountof the composition of the filler and the resin-forming compound(monomer) such as compound of the formula (II) or (III).

If the inorganic filler is pretreated with a keying agent, such asγ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane and so forth,the bond between the formed resin and the inorganic filler will beintensified and the physical properties as a material for medical ordental use will be further improved.

The monomer of the present invention represented by the said formula(II) or (III) is readily polymerized and cured by means of a catalyst.On this occasion, the application of heat often does harm to the humanbody and it is preferred to divide the said monomer, into two, liquidportions one containing a catalyst and the other containing anactivator, in such a manner that the monomer can be cured at normaltemperature by mixing both liquids immediately prior to use.

As the catalyst, peroxide is preferred and it should preferably be usedin combination with the activator. As the peroxide catalyst, there canbe cited, for instance, diacyl peroxides, such as benzoyl peroxide,parachlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, acetylperoxide, lauroyl peroxide and so on, hydroperoxides, such as tertiarybutyl hydroperoxide, cumene hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide and so on, ketone peroxides, suchas methyl ethyl ketone peroxide and so on, peroxycarbonates, such astertiary butyl peroxybenzoate and so on, etc.

These peroxide catalysts should preferably be used in proportions of0.1-2.5% by weight based on the total weight of the polymerizablemonomers of the present invention represented by the said formula (II)or (III).

As the activator capable of use in combination with the peroxide, therecan be cited, for instance, tertiary amines, such asN,N-bis-(2-hydroxyethyl)-4-methylaniline,N,N-bis-(2-hydroxyethyl)-3,4-dimethylaniline,N,N-bis-(2-hydroxyethyl)-3,5-dimethylaniline,N-methyl-N-(2-hydroxyethyl)-4-methylaniline, 4-methylaniline,N,N-dimethyl-p-toluidine, N,N-dimethylaniline, triethanolamine and soon, and in addition, transition metal ions, such as cobalt naphthenate,cobalt octanate and so on, amine salts of p-toluenesulphonic acids andsulphinic acids and so forth.

These activators can generally be used in proportions of 0.1 to 2.5% byweight based on the total weight of the said polymerizable monomers.

The monomer of the present invention can also be polymerized and curedby irradiation of ultraviolet rays. In this case, it is not necessary toformulate the composition into the said two-liquid form and it ispreferred to use a photosensitizer in the amount of 0.1-10% by weightbased on the total weight of the polymerizable monomers. As thephotosensitizer, there can be cited, for instance, carbonyl compounds,such as benzoin, benzoin methyl ether, benzoin ethyl ether, acetoin,benzophenone, p-chlorobenzophenone, p-methoxybenzophenone and so on,sulphur compounds, such as tetramethylthiuranium monosulphide,tetramethylthiuranium disulphide and so on, azo compounds, such asazobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile and so on,peroxide compounds, such as benzoyl peroxide, tertiary butyl peroxideand so on, etc.

For the enhancement of the preservability of the resin composition, itis effective to add an UV absorber such as benzophenone type compound,such as 2-hydroxy-4-methylbenzophenone, in an amount of 0.5-2.0 parts byweight, based on 100 parts by weight of the resin composition, or astabilizer generally called a free radical inhibitor, such asp-methoxyphenol, 2,5-di-tert.butyl-4-methylphenol and so on, in anamount of 0.05-0.20 part by weight, based on 100 parts by weight of theresin composition.

For a method of using such resin compositions, it is very convenient toprepare in advance a first paste-like substance (paste A) comprising aninorganic filler, resin composition and activator and second paste-likesubstance (paste B) comprising an inorganic filler, resin compositionand catalyst, for instance, since the polymerization is initiated uponmixing there two pastes when used by doctors.

In the case of using such material in the restoration of the hard tissueof the human body, such as teeth and bones, the said material possessessufficient bonding to the hard tissue, but it is also effective to applythe said material after precoating the hard tissue with a bonding agentin ordinary use, such as 2-hydroxyethylmethacrylate and so on, for thepurpose of improving the bonding to the hard tissue. As the said bondingagent, the subject matter of another co-pending Patent Application Ser.No. 138,815 filed Apr. 9, 1980 claiming the priority based on JapanesePatent Application No. 54-44751, discovered by the instant inventors,can be very effectively used, which bonding agent consists predominantlyof a composition comprising 50-99.5% by weight of polymerizable acrylateesters and/or methacrylate esters having hydrophilic groups comprisingcarboxyl, epoxy, amine or hydroxyl, and 0.5-50% by weight of at leastone member of organic metal compounds selected from the group consistingof alkoxy-containing titanium compounds and silicon compounds.

Thus, according to the present invention there can be obtained resincompositions suitable for medical or dental use which are extremelyexcellent in various physical properties after curing, such as hardness,compressive strength, abrasion resistance, weak in tissue irritation andgood in bonding to the hard tissue of the human body and on top of that,excellent in operation in practical use.

Further, the resin-forming material of the present invention can beadvantageously used, in medical or dental use, not only as a materialfor bone cement and artificial bones in the orthopedic surgery andrestorative surgery field, but also as a restorative material for crownbridges, core material for crowns, dental cement, filling material,cavity lining material, root canal filling material and so on, in theoperative dentistry and prosthetic dentistry field in particular.

In the following, explanations will be given of implant materials of thepresent invention for medical or dental use, viz., for the human body.

As typical examples of composite resin-forming material obtained from acombination of conventional resin-forming material and inorganic filler,there can be cited, for instance, bone cement and artificial bonematerial in the orthopedic surgery and restorative surgery field orrestorative material for crown bridges, core material for crowns, dentalcement, filling material, cavity lining material, root canal fillingmaterial and so forth in the operative dentistry and prothetic dentistryfield.

This composite resin for medical or dental use has excellent functionsas compared to the direct filling resin and inorganic cementsconventionally used in the above fields in the points of bonding, waterresistance, compressive strength, abrasion resistance and impactresistance, in particular.

In the case of curing by applying the conventional compositeresin-forming material for dental use to molars in the operativedentistry and prosthetic dentistry field, for instance, clinicalexamples show that the form is lost in a short period of time because ofthe markedly high occlusal pressure and frictional force in the molarand that it is difficult to use it stably over a long period of time. Inorder to make it applicable to molars, there is demanded a compositeresin for dental use having higher mechanical strengths, such ascompressive strength, abrasion resistance, impact resistant function andso on. Conventionally, metal material and dental amalgam are mainly usedin the molars, but the metal material presents a problem in the point ofconvenience, whereas the dental amalgam, on the other hand, leaves aproblem to solve in the point of toxicity and of recurrent caries causedfrom the property inherent in the amalgam and, for these reaons, it isnot satisfactory material.

The composite resin suitable for medical or dental use is usually madeup of a mixture of resin-forming material and various powdery fillers,such as powdered quartz filler, powdered borosilicate glass filler andso on, but because it is affected, in particular, by a low degree ofhardness and the abrasion resistant function these powdery fillerspossess, the composite resin obtained was not of the high mechanicalstrength and high abrasion resistance, in particular, required of it inthe practical aspect, no matter what resin-forming material might beused.

Of conventionally known fillers, however, powdered alumina filler showsexceptionally high hardness and abrasion resistance. Alumina is amaterial which is excellent in abrasion resistance, having a Mohs'hardness of 9, but because of inferior bonding to the resin for medicalor dental use, a satisfactory resin-forming material for medical ordental use cannot be obtained, even if it is subjected to varioussurface treatments.

The instant inventors found that the metal nitrides specified below, ascompared to various conventional powdered fillers, have a higher degreeof hardness and abrasion resistance and better bonding to the resin formedical or dental use and accordingly, have much higher mechanicalstrengths, such as compressive strength, abrasion resistance or impactresistance, when used in the composite resin-forming material.

The present invention is designed to provide an implant materialsuitable for medical or dental use, a composite resin-forming materialcontaining such implant material (or filler) and which possessesextremely high mechanical strengths applicable to all medical fields,such as the orthopedic surgery and restorative surgery field or theoperative dentistry and prosthetic dentistry field and so on.

According to the present invention, the said purposes and merits couldbe achieved by the restorative implant material of the human bodycharacterized by comprising nitride of at least one member of metalselected from the group consisting of Group IVB, Group VB and Group VIBin the Periodic Table of elements and boron, aluminum and silicon, andhaving a Mohs' hardness of at least 7.

The said metal nitride may contain a nitride of a metal other than thesaid metals enumerated above, such as nickel, cobalt and manganese,provided that it is as small an amount as about 10% or less, and 5% orless, in particular, based on the amount of the said metal nitride. Evenin such cases, it is necessary for the nitride to have an overall Mohs'hardness of at least 7 and preferably at least 9.

The metal forming the nitride of the present invention is at least onemember of metals selected from the group consisting of titanium,zirconium, hafnium (the foregoing belong to Group IVB of the PeriodicTable), vanadium, niobium, tantalum (the foregoing belong to Group VB ofthe Periodic Table), chromium, molybdenum, tungsten (the foregoingbelong to Group VIB of the Periodic Table), boron, aluminum and silicon.

Of the said metal nitrides, particularly preferred in the presentinvention is the nitride of at least one member of metals selected fromthe group consisting of vanadium, boron, aluminum and silicon. Nitrideof silicon, in particular, is preferred since it is high in hardness,great in bondability to the resin-forming material and its cured resin,and said nitride is economically low in cost.

The said metal nitride of the present invention should advantageouslyhave a Mohs' hardness of at least 9, in particular.

The said metal nitride, the implant material of the present invention,may be used in any form, such as rods, pellets, powder and so on, but itis preferred to use it as a composite resin-forming material by mixingit in powder form, in particular, to the one of the resin-formingmaterials (monomers) for medical or dental use, either theconventionally known monomers or the monomers belonging to the presentinvention.

The said metal nitride of the present invention can fully exhibit thiseffect even if it is used in combination with materials applicable tothe orthopedic surgery and restorative surgery field or the operativedensitry and prosthetic dentistry field, other than the resin-formingmaterial, such as the conventionally known zinc phosphate cement, andsilicate cement.

The restorative implant material for the human body of the presentinvention should preferably be in powder form, in particular, and itsparticle diameter should preferably fall in the range of 50 microns orless and 0.1-50 microns, in particular. If the particle size is lessthan 0.1 micron, in some cases, the paste comprising the compositeresin-forming material in an uncured condition may overly increase inviscosity. If it is in excess of 50 microns, on the contrary, the resinand filler tend to readily separate from each other after being mixedtogether. In some cases, it is practically rendered difficult tooperate. The implant material material of the present invention shouldhave Mohs' hardness of 7 or more, but preferably it should have Mohs'hardness of 9 or more. If the hardness is less than 7, the purpose ofthe present invention cannot be achieved in the aspect of physicalproperties obtained when using it as a composite substance mixed withthe resin. In this connection, of the implant materials of the presentinvention, as those which have a Mohs' hardness of 9 or more there canbe cited BN, Si₃ N₄ and VN. Further, aluminum nitride is somewhat lowerin Mohs' hardness than the said nitrides, but those with Mohs' hardnessof about 8 can be obtained with relative ease and hence, aluminumnitride is preferable.

In the case, in particular, of using as a restorative material for crownbridge or filling material in a molar tooth in the operative dentistryand prosthetic dentistry field, particularly high compressive strengthand abrasion resistance are required since it must withstand highocclusal pressure. In this case, therefore, the implant material shouldpreferably have a Mohs' hardness of 9 or more. In the case, further, ofusing the implant material of the present invention as a filler formedical or dental use, in particular, it should advantageously beprecoated with a keying agent prior to use. As such a keying agent, anyknown ones are useful, but a silicon-containing keying agent isparticularly preferred. As such a silicon-containing keying agent, thereare particularly preferred silicon-containing organic compoundspossessing at least three alkoxy groups, inter-alia, silicon-containingorganic compounds possessing at least three alkoxy groups and oneorganic group containing, as a terminal group, a mono-olefinichydrocarbon residue, primary amino group or epoxy group. As the typicalones of such preferred keying agents, there can be citedα-methacryloxypropyltrimethoxysilane or vinyl-triethoxysilane.

By coating the said powdered metal nitride with such keying agents thebond between the powder of the said metal nitride and the resin-formingmaterial (or its cured resin) for medical or dental use is intensified,the property of the composite resin-forming material for medical ordental use is improved and the fluidity characteristic is improved whenmixing both together and the filler content can be increased.

In the case of using the filler for medical or dental use belonging tothe present invention by mixing same with the resin-forming material(monomer) for medical or dental use to form composite resin-formingmaterial for medical or dental use, for proportions in which it isincorporated, the said filler should preferably be set at 50-95% byweight, and 70-90% by weight, in particular, and the resin-formingmaterial for medical or dental use at 5-40% by weight, and 10-25% byweight, in particular. If the filler is used in on amount of less than50% by weight, the composite resin obtained will be lowered in physicalproperty values, such as compressive strength, abrasion strength and soon, whereas if it is in excess of 95% by weight, the composite resinpaste in an uncured condition will be higher in viscosity and inferiorin operation.

As the resin-forming material (monomer) for medical or dental usecapable of being mixed with the metal nitride filler belonging to thepresent invention any conventionally known ones are available.

As such resin-forming material (monomer) for medical or dental use, anyones are available which are conventionally known to be usable in thisfield. Typical ones will be illustrated as follows.

(1) Polycarbinol polymethacrylates disclosed in U.S. Pat. Nos. 3,541,068and 3,597,389, etc.:

(2) 2,2-Bis-[p-(β-oxyethoxy)phenyl]-propanedimethacrylate (hereinaftercalled the Bis-MEPP for short) type monomers represented by thefollowing formula (4) as disclosed in U.S. Pat. Nos. 3,810,938;3,923,740; 4,067,853, etc.: ##STR7## wherein R stands for a hydrogenatom or a methyl group;

X stands for an alkylidene or a --SO₂ -- group;

Y stands for an oxyalkylene group having between 2 and 5 carbon atoms oran alkylidene group containing between 1 to 5 carbon atoms.

(3) Trimethylolpropane trimethacrylate (TMPT) type monomers representedby the following formula (5) disclosed in British Patent No. 1,451,262:##STR8## wherein R₁ is CH₃ --, CH₃ CH₂ -- or CH₃ CH₂ CH₂ --, and R₂ is Hor --CH₃.

(4) Urethane diacrylate type monomers represented by the followingformula (6) as disclosed in U.S. Pat. Nos. 3,825,518; 3,862,920, etc.:##STR9## wherein R₁ is a hydrogen atom or a methyl group, R₂ is analkylene group and R₃ is a divalent hydrocarbon radical.

(5) Monomers of the type represented by the following formula (7) asdisclosed in the U.S. Pat. No. 3,853,962, etc.: ##STR10## (6)Neopentylglycol dimethacrylate (NPG) type monomers as disclosed inJapanese Laid-Open Patent Application (JAPAN KOKAI) No. 48-90332.

(7) Triethyleneglycol dimethacrylate (TEG) type monomers as disclosed inJapanese Laid-Open Patent Application (JAPAN KOKAI) No. 50-116581.

By formulating the composite resin-forming material by combiningtogether at least one member of compounds (monomer) of the presentinvention represented by the said formulae (I), (II) and (III) and thesaid metal nitride (implant material), besides the said knownresin-forming material (monomer) for medical or dental use, it ispossible to form composite resin compositions which are further improvedin mechanical properties, such as compressive strength, abrasionresistance and so on.

The method of compounding of at least one member of compounds (monomer)of the present invention represented by the formulae (I), (II) and (III)and the said metal nitride filler, as well as the preparation and curingof that paste, it is the same as described for the case of compoundingthe said compound (monomer) and conventional inorganic filler.

The composite resin-forming material using the filler-forming materialfor medical or dental use belonging to the present invention contains,in practical use, usually a catalyst for the polymerization of theresin-forming material and an activator for the formation of freeradicals by the reaction of the catalyst besides, in addition to thefiller and the resin-forming material. Explanations were already givenof these catalysts and activators.

For a method for use of such composite resin-forming material based onpractical use, for instance, a paste-like substance (paste A) comprisingthe filler belonging to the present invention, preferably said powderyfiller, resin-forming material (monomer) and an activator and apaste-like substance (paste B) comprising the filler belonging to thepresent invention, resin-forming material (monomer) and a catalyst couldbe prepared in advance and these two pastes can be mixed together whenused by doctors or dentists. The composition can be used with goodefficiency since the resin is cured with the polymerization initiatedupon their mixing.

When using the said metal nitride of the present invention as a filler,in some cases the storage stability of the paste (paste B) maydeteriorate according to the kind of the metal nitride if it is broughtin contact with the catalyst for a long time.

In such cases, it is advantageous to use, as the filler for the paste A,the metal nitride of the present invention and to use as the filler forthe paste B an inorganic filler capable of forming a stable paste evenif it is maintained in contact with a conventional catalyst, such aspowdered α-quartz, in such a manner that the metal nitride in the pasteA should account for at least 50% by weight, preferably at least 70% byweight, and more preferably at least 80% by weight, based on the totalamount of fillers including the inorganic filler in the paste B. Bycombining together both pastes in such a manner, a cured composite resincomposition is formed therefrom which is stable to storage and extremelyexcellent in mechanical characteristics.

The composite resin composition which underwent curing treatment, usingthe filler for medical or dental use belonging to the present invention,shows excellent mechanical strengths, such as extremely high compressivestrength, abrasion resistance, impact resistance and so on, and it isreadily applicable according to usage to every field of medical use,such as the orthopedic surgery and restorative surgery field or theoperative dentistry and prosthetic dentistry field and so on.

The implant material of the present invention can be used alone and inaddition, as a composite composition with any resin-forming material formedical or dental use. Not only that, but as mentioned earlier, even ifit used by mixing with self-curing compositions, such as silicatecement, zinc phosphate cement and so on, its physical property values,such as compressive strength, abrasion resistance and so on, can beimproved.

The present invention will be specifically explained with the referenceto working examples as follows. Unless otherwise specified, "part" and"%" in the examples mean "part by weight" and "% by weight". Further, inthe examples the composition of the resin-forming material (monomer) andfiller prior to curing treatment is called the "composite resin" forshort for convenience's sake.

In this connection, in the examples the method for the preparation ofthe composite resin and methods for the measurement of compressivestrength, abrasion, water sorption, hardness, toothbrush abrasion,coloring, linear thermal expansion coefficient, and tensile strengthfollow the hereinafter-described procedures.

(1) A method for the preparation of composite resin:

(1)-1. Preparation of filler:

100 gr. of powdery filler classified to a particle size of 50 microns orless was mixed in an aqueous solution obtained by vigorously mixing 10 gof γ-methacryloxypropyltrimethoxysilane and 1 ml of acetic acid withagitation by addition of 200 ml of water and the powdery filler wasseparated after agitation. Powdery filler so separated was dried in ahot air dryer held at 105° C. for 24 hours whereby a silane-treatedfiller was prepared.

In the Examples, the fillers were all treated with silane and then used.

(1)-2. Preparation of monomer paste:

Monomer was divided into two equal parts, one monomer was incorporatedwith a polymerization activator and the filler prepared by the procedureof (1)-1 above (hereinafter called Paste A for short) and the othermonomer was incorporated with a catalyst and a filler prepared by theprocedure of (1)-1 (hereinafter called Paste B for short).

In the Examples, N,N-bis-(2-hydroxyethyl)-4-methylaniline was used asthe activator and benzoyl peroxide was used as the catalyst.

For the amount in which the activator was mixed to Paste A and theamount in which the catalyst was mixed to Paste B, they were formulatedin such a manner that curing should occur about 3 minutes after mixingPaste A and Paste B.

(1)-3. Preparation of composite resin:

Paste A and Paste B were taken each in equal amounts, mixed and kneadedtogether on a kneading paper at room temperature for 30 seconds wherebya composite resin was prepared.

(2) Measurement of compressive strength:

Based on American Dental Association (ADA) Specification No. 9 forDental Silicate Cement, compressive strength was measured by thefollowing procedures.

Composite resin was loaded in a mould, sealed with sheeted glass, thenplaced in a pressure vessel and left to stand under an atmosphere of 37°C. and relative humidity of 100% for 15 minutes. The cured compositeresin was taken out from the mould and immersed in water held at 37° C.for 24 hours whereby specimens were prepared. By using one Instrontester, the specimens were pressed at conditions of press rate of 0.2mm/min. to determine their compressive strength.

(3) Measurement of abrasion loss:

Cured composite resin loaded in and taken out from the mould byfollowing the procedures set forth in section of "(2) Measurement ofcompressive strength" was used as specimens for measurement of abrasionloss. The specimens were dried in a hot air dryer held at 100° C. for 24hours and then cooled in a desiccator for one hour and weighed. Thespecimens were placed in a cylindrical metal ball mill with an innercapacity of 500 ml and inner diameter of 10 cm and simultaneously, 20stainless steel balls of 1 mm diameter and 200 ml of polishing pasteprepared by adding 900 parts by weight of distilled water to 200 partsby weight of powdered Si₃ N₄ passing through a 325 mesh sieve, as apolishing material, were loaded, the ball mill was sealed and thenrotated at a rate of 100 r.p.m. for 78 hours. After it was finished, thespecimens were washed with water, dried in the hot air dryer held at100° C. for 24 hours and cooled in the desiccator for another one hourand weighed. Abrasion loss was calculated according to the followingequation: ##EQU1##

(4) Measurement of amount of water sorption:

Based on American Dental Association (ADA) Specification No. 27 forDirect Filling Resins, the amount of water absorbed was measured by thefollowing procedure.

Composite resin was cured to prepare a disk specimen 20 mm across and 1mm thick. The specimen was left to stand in a constant temperature dryerheld at 37° C., then placed in the desiccator, cooled for one hour andweighed. Value when a constant quantity was reached with repetition ofthis operation was set as dry weight. Then, the specimen was immersed inwater held at 37° C. for 7 days, then taken out, the water on thesurface was wiped off with soft gauze and the specimen was weighed todetermine the weight of water absorbed. The amount of water absorbed wascalculated by the following equation: ##EQU2##

(5) Measurement of hardness:

Measurement was made of Knoop hardness by means of a microhardnesstester of Shimagu make. Composite resin was cured to prepare a columnarspecimen 10 mm across and 5 mm high and a load of 900 g was applied onthe flat surface of the specimen for 15 minutes. The length of the dentformed on the surface of the specimen was measured to determine theKnoop hardness.

(6) Toothbrush abrasion test:

Composite resin was cured to prepare and fix a columnar specimen 13 mmacross and 4 mm high. A commercially available toothbrush with a load of200 g was applied to the flat portion of the specimen and thistoothbrush was reciprocated at a stroke of 2 reciprocations/second topolish the specimen surface. In the meantime, a solution prepared bydiluting 150 g of commercially available toothpaste to 1/2 with waterwas continuously added dropwise. After 8 hours the specimen was washedwith water, dried and weighed. Rate of toothbrush abrasion loss wascalculated by the following equation. ##EQU3##

(7) Coloring test:

Disk test pieces 13 mm across and 4 mm high were surface-polished withNo. 800 emery paper and then immersed in commercially available aqueouscoffee solution (solution obtained by dissolving 2.5 g of powderedcoffee in 100 ml of water) at 37° C. for 4 days. The specimens werewashed with water, dried and then their color was measured by means of acolorimeter, a product of Nippon Denshoku Kogyo company, to read thevalues L, a and b. Likewise, the values L₀, a₀ and b₀, which were themeasured color values of the specimen surfaces prior to immersing intothe coffee solution, were read, the degree of discoloration ΔE wascalculated by the following equation and ΔE was set as a basis forcoloring. The greater is the value of ΔE, the greater is the degree ofdiscoloration. This test was also effected on the surface of theunpolished specimen.

    ΔE=√(L-L.sub.0).sup.2 +(a-a.sub.0).sup.2 +(b-b.sub.0).sup.2

(8) Measurement of linear thermal expansion coefficient:

Composite resin was enclosed in a glass tube 5 mm in diameter and 20 mmin length, the opening of the tube was sealed with a cover glass formicroscope, left to stand at room temperature for 15 minutes and thenthe cured composite resin was taken out from the glass tube wherebyspecimens for measurement were prepared.

Measurement was made of the linear thermal expansion coefficient of thespecimens so prepared by means of linear thermal expansion measuringinstrument, a product of Rigsku Denki company. In making themeasurements the heating and temperature raising rate was set at 5°C./min.

(9) Measurement of tensile strength:

Based on pressure tear test according to ADA Specification No. 27 forthe diametrial method, the tensile strength was measured by thefollowing procedure.

Composite resin was loaded in a stainless steel mould 6 mm in innerdiameter and 3 mm in height and the opening of the mould was sealed witha cover glass for a microscope. The mould was left to stand under anatmosphere of 37° C. and relative humidity of 95% for 15 minutes. Afterthat, the cured composite resin was taken out from the mould. This curedcomposite resin was polished by use of powdered SiC and then immersed inthe water held at 37° C. for 24 hours whereby specimens for measurementwere prepared.

Tensile strength of the specimens so prepared was measured by means ofan Instron tension tester. In making the measurements, the head pressrate was set at 1 cm/min.

EXAMPLE 1

Silane-treated α-SiO₂ was prepared following the procedure for thepreparation of filler in section (1)-1. Then, using mixed monomers, asthe monomer component, prepared by mixing tetramethylolmethanetriacrylate (TMM-3A) and tetramethylomethane tetracrylate (TMM-4A) inproportions of 55:45 (by weight ratio), silane-treated α-SiO₂, catalystand activator, the mixed monomer was divided into two equal parts forthe preparation of Paste Al-1 and Paste Bl-1 of the followingcompositions according to the procedure for the preparation of monomerpaste in section (1)-2.

Paste Al-1 and Paste Bl-1 so prepared were taken each in equal amounts,mixed and kneaded together on kneading paper at room temperature for 30seconds whereby a composite resin was prepared.

This composite resin was loaded in a stainless steel pipe with innerdiameter of 10 mm and height of 5 mm at one end and the excess part wasremoved off with sheeted glass. An injection needle was stuck into thesurface of the composite resin at intervals of 10 seconds at roomtemperature to measure the curing time. It was about 3 minutes long.

    ______________________________________                                                               Part by weight                                         ______________________________________                                        Paste A1-1                                                                    Tetramethylolmethane triacrylate (TMM-3A)                                                              55                                                   Tetramethylolmethane tetracrylate (TMM-4A)                                                             45                                                   Silane treated α-SiO.sub.2                                                                       300                                                  N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                              0.8                                                  Paste B1-1                                                                    Tetramethylolmethane triacrylate (TMM-3A)                                                              55                                                   Tetramethylolmethane tetracrylate (TMM-4A)                                                             45                                                   Silane treated α-SiO.sub.2                                                                       300                                                  Benzoyl peroxide         0.8                                                  ______________________________________                                    

Compressive strength, abrasion loss and bonding strength were measuredof the composite resin and results were shown in Table 1.

Paste A's and Paste B's of following compositions were formulated usingvarious monomers conventionally known as resin-forming material formedical or dental use instead of the mixed monomer of TMM-3A and TMM-4A.

    ______________________________________                                                               Part by weight                                         ______________________________________                                        Paste A1-2                                                                    Bisphenol A diglycidyl methacrylate (Bis-GMA)                                                          80                                                   Triethyleneglycol dimethacrylate (TEGDMA)                                                              20                                                   Silane treated αSiO.sub.2                                                                        300                                                  N,N--bis(2-hydroxyethyl)-4-methylaniline                                                               0.8                                                  Paste B1-2                                                                    Bisphenol A diglycidyl methacrylate (Bis-GMA)                                                          80                                                   Triethyleneglycol dimethacrylate (TEGDMA)                                                              20                                                   Silane treated αSiO.sub.2                                                                        300                                                  Benzoyl peroxide         0.8                                                  Paste A1-3                                                                    Bismethacryloxyethoxydiphenylpropane                                                                   100                                                  (Bis-MEPP)                                                                    Silane treated α-SiO.sub.2                                                                       300                                                  N,N--bis(2-hydroxyethyl)-4-methylaniline                                                               1.0                                                  Paste B1-3                                                                    Bismethyacryloxyethoxydiphenylpropane                                                                  100                                                  (Bis-MEPP)                                                                    Silane treated α-SiO.sub.2                                                                       300                                                  Benzoyl peroxide         1.0                                                  Paste A1-4                                                                    Neopentylglycol dimethacrylate (NPGDMA)                                                                100                                                  Silane treated αSiO.sub.2                                                                        300                                                  N,N--bis(2-hydroxyethyl)-4-methylaniline                                                               2.0                                                  Paste B1-4                                                                    Neopentylglycol dimethacrylate (NPG-DMA)                                                               100                                                  Silane treated αSiO.sub.2                                                                        300                                                  Benzoyl peroxide         2.0                                                  Paste A1-5                                                                    Trimethylolpropane triacrylate (TMPT)                                                                  100                                                  Silane treated α-SiO.sub.2                                                                       300                                                  N,N--bis(2-hydroxyethyl)-4-methylaniline                                                               1.5                                                  Paste B1-5                                                                    Trimethylolpropane triacrylate (TMPT)                                                                  100                                                  Silane treated αSiO.sub.2                                                                        300                                                  Benzoyl peroxide         1.5                                                  ______________________________________                                    

These Paste A's and Paste B's corresponding to sub-numbers were takeneach in equal amounts and various composite resins were preparedfollowing the same procedures as the above. Compressive strengths,abrasion loss and bonding strengths were measured of these curedcomposite resins. Results were shown in Table 1:

                                      TABLE 1                                     __________________________________________________________________________                                       Bonding strength                                            Amount of                                                                           Compressive                                                                          Abrasion                                                                           (kg/cm.sup.2)                                               filler used                                                                         strength                                                                             loss Bovine                                                                            Bovine                                 Monomer composition tested*.sup.1                                                              (α-SiO.sub.2)*.sup.2                                                          (kg/cm.sup.2)                                                                        (cm.sup.3)                                                                         enamel                                                                            dentin                                 __________________________________________________________________________     1                                                                              TMM-3A(55)/TMM-4A(45)                                                                        75 wt. %                                                                            2,570  0.49 60-70                                                                             15-20                                  2*                                                                              Bis-GMA(80)/TEG(20)                                                                          "     2,100  0.62 30-40                                                                             0-5                                    3*                                                                              Bis-MEPP       "     2,290  0.59 --  --                                     4*                                                                              NPGDMA         "     2,180  0.57 --  --                                     5*                                                                              TMPT           "     2,440  0.62  5-10                                                                             0                                      __________________________________________________________________________     NOTE                                                                          *.sup.1 In the case of mixed monomer, parenthesis () following upon a         short form for each monomer indicates a weight ratio of the monomer. (The     same will apply to the respective tables in the hereinafterdescribed          Examples.)                                                                    *.sup.2 The amount of filler used indicates a percentage by weight of the     filler based on the total amount of the monomer and the filler. (The same     will apply to the respective tables in the hereinafterdescribed Examples.     *Indicates Control and the same will apply to the respective tables in th     hereinafterdescribed Examples.                                           

It follows from the above table that the composite resin (Run No. 1)comprising the monomer composition of TMM-3A(55)/TMM-4A(45) belonging tothe present invention should be excellent in compressive strength,abrasion loss and bonding strength as compared to the composite resinsof Run Nos. 2-5 comprising the monomer compositions of Bis-GMA/TEG,Bis-MEPP, MPGDMA or TMPT conventionally known as resin-forming monomersfor medical or dental use.

Bonding strength was measured by the following procedure.

(1) Bonding strength to bovine dentin:

A fresh anterior bovine tooth implanted into a square rod made of acrylresin was polished with emergy paper until the dentin was exposed, andfurther polished and finished with No. 800 emery paper for the formationof a contact surface whereby there was prepared a test-piece of materialfor the bonding test with the bovine dentin. This bonding testpiece wasstored in water. It was taken out from the water immediately before themeasurement was made. The surface of the testpiece was well wiped offand further dried in a weak air stream. Then, the bonding surface of thebovine dentin was coated with composite resin and the square rod made ofacryl resin was stuck and pressed against the coated surface. It wasleft to stand at room temperature for 15 minutes and then immersed inwater held at 37° C. for 24 hours. Both ends of the acryl resin squarerods of the specimen were pulled apart at a rate of 1 mm/min. todetermine the bonding strength. The bonding strength was indicated bythe maximum value and the minimum value of measured numericals whenmeasuring the respective specimens for every 20 testpieces.

(2) Bonding strength to bovine enamel:

A fresh anterior bovine tooth implanted in a square rod made of acrylresin was polished and leveled with emery paper, and further polishedand finished with No. 800 emery paper for the formation of a bondingsurface whereby there was prepared a testpiece of material for thebonding test with the bovine enamel. This bonding testpiece was storedin water. It was taken out from the water immediately before themeasurement was made. The surface of the testpiece was well wiped offand etched with 50% aqueous phosphate solution for one minute. It wassuccessively washed with water and air dried using a weak air stream.Using the testpiece of material for the bonding test with the bovineenamel so prepared, its bonding strength was measured following the sameprocedure as in the case of the measurement of the bonding strength withthe bovine dentin and the measured values were indicated in the samemanner.

EXAMPLE 2

Using, as the monomer, mixed monomers prepared by mixing TMM-3A andTMM-4A in various such proportions as indicated in Table 2, Paste A 2and Paste B 2 of following compositions were prepared. Paste A 2 andPaste B 2 were mixed and kneaded together following the same procedureas set forth in Example 1 whereby composite resins were prepared.

    ______________________________________                                                              Part by weight                                          ______________________________________                                        Paste A 2                                                                     TMM-3A                      100     in total                                  TMM-4A                                                                        Silane treated α-SiO.sub.2                                                                      300                                                   N,N--bis(2-hydroxyethyl)-4-methylaniline                                                              0.1                                                   Paste B 2                                                                     TMM-3A                      100     in total                                  TMM-4A                                                                        Silane treated α-Sio.sub.2                                                                      300                                                   Benzoyl peroxide        1.0                                                   ______________________________________                                    

Compressive strength, abrasion loss, amount of water sorption andbonding to bovine tooth were measured of these cured composite resins.Results were shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                 Amount of                                                                           Compressive                                                                          Abrasion                                                                           Amount of                                                                             Bonding strength                       Monomer composition                                                                        filler used                                                                         strength                                                                             loss water sorption                                                                        (kg/cm.sup.2)                          TMM-3A TMM-4A                                                                              (α-SiO.sub.2)                                                                 (kg/cm.sup.2)                                                                        (cm.sup.3)                                                                         (mg/cm.sup.2)                                                                         (to bovine dentin)                     __________________________________________________________________________    1 100   0    75 wt. %                                                                            2,410  0.55 0.38    15-20                                  2 90   10    "     2,480  0.54 0.36    15-20                                  3 70   30    "     2,490  0.50 0.30    10-15                                  4 50   50    "     2,520  0.48 0.30    10-15                                  5 30   70    "     2,550  0.48 0.33     5-10                                  6 10   90    "     2,500  0.52 0.33     5-10                                  7  0   100   "     2,450  0.53 0.37    0-5                                    __________________________________________________________________________

It is noted from the above table that either triacrylate (TMM-3A) ortetracrylate (TMM-4A) will suffice for the monomer constituting thecomposite resin of the present invention. The bonding strength valueincreases in proportion to the increased amount of TMM-3A mixed. Forthis reason it is conceived that because TMM-3A possesses one moremethylol group (--CH₂ OH) than the triacrylate ester, this additionalmethylol group contributes to the bonding with the hard tissue of thehuman body.

In the case of the mixed monomer using a combination of TMM-3A andTMM-4A and the mixed monomer prepared by mixing them together inproportions of 30-70 parts by weight of TMM-3A and 70-30 parts by weightof TMM-4A, in particular dental composite resin could be advantageouslyformed which is excellent in the bonding with the hard tissue of thehuman body with excellent compressive strength.

In the case, further, of using TMM-3A and TMM-4A in combination,composite resin formed therefrom is found to show very excellent waterresistance besides the said characteristics.

EXAMPLE 3

Composite resins were prepared following the same procedures of Example1 except that there were used the mixed monomer of TMM-3A(55)/TMM-4A(45)belonging to the present invention or conventionally known mixed monomerof Bis-GMA(80)/TEG(20) as the resin-forming monomer, given amounts ofvarious inorganic metal oxides conventionally known as the dentalinorganic filler listed in Table 3 below as the filler, catalyst andactivator in such amounts as set forth in the Table 3. Comparativestength and abrasion loss were measured of these cured composite resins.Results were tabulated in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                             Amount of                                                                           Amount of                                                               activator                                                                           catalyst                                                       Filler   (part/100                                                                           (part/100                                                                           Compressive                                                                          Abrasion                                              Amount                                                                             parts of                                                                            parts of                                                                            strength                                                                             loss                              Monomer composition                                                                           Kind                                                                              (wt %)                                                                             monomer)                                                                            monomer)                                                                            (kg/cm.sup.2)                                                                        (cm.sup.3)                        __________________________________________________________________________     1                                                                               TMM-3A(55)/TMM-4A(45)                                                                      Al.sub.2 O.sub.3                                                                  75   0.8   1.0   2,570  0.47                              2 "             ZrO.sub.2                                                                         70   1.0   1.5   2,500  0.47                              3 "             ZrSiO.sub.4                                                                       75               2,700  0.43                              4*                                                                              Bis-GMA(80)/TEG(20)                                                                         Al.sub.2 O.sub.3                                                                  75   0.8   1.0   2,100  0.60                              5*                                                                              "             ZrO.sub.2                                                                         70               2,040  0.58                              6*                                                                              "             ZrSiO.sub.4                                                                       75               2,200  0.55                              __________________________________________________________________________     *indicates Control.                                                      

It is noted from the above table that if various metal oxidesconventionally known as dental inorganic filler are used in combinationwith conventionally known Bis-GMA type monomers, they will not be fullysatisfactory in the point of compressive strength and abrasionresistance, whereas the monomer belonging to the present invention, evenif used in combination with these metal oxides, will show fullysatisfactory compressive strength and abrasion resistance.

EXAMPLE 4

Using, as the composite resin-forming monomer, TMM-3A(55)/TMM-4A(45) ortetramethylolmethane trimethacrylate (TMM-3M)(55)/tetramethylolmethanetetramethacrylate (45) Paste A 4-1, B 4-1 and Paste A 4-2 and B 4-2 offollowing compositions were prepared. Following the same procedure asthat of Example 1 these pastes were mixed for the preparation ofcomposite resins.

    ______________________________________                                                                 Part                                                                          by weight                                            ______________________________________                                        Paste A4-1                                                                    TMM-3A                     55                                                 TMM-4A                     45                                                 Silane treated α-SiO.sub.2                                                                         456                                                N,N--bis(2-hydroxyethyl)-4-methylaniline                                                                 0.8                                                Paste B4-1                                                                    TMM-3A                     55                                                 TMM-4A                     45                                                 Silane treated α-SiO.sub.2                                                                         456                                                Benzoyl peroxide           1.0                                                Paste A4-2                                                                    Tetramethylolmethane trimethacrylate (TMM-3M)                                                            55                                                 Tetramethylolmethane tetramethacrylate (TMM-4M)                                                          45                                                 Silane treated α-SiO.sub.2                                                                         456                                                N,N--bis(2-hydroxyethyl)-4-methylaniline                                                                 0.8                                                Paste B4-2                                                                    Tetramethylolmethane trimethacrylate (TMM-3M)                                                            55                                                 Tetramethylolmethane tetramethacrylate (TMM-4M)                                                          45                                                 Silane treated α-SiO.sub.2                                                                         456                                                Benzoyl peroxide           1.0                                                ______________________________________                                    

Compressive strength, abrasion loss and amount of water sorption weremeasured of these cured composite resins results were tabulated in Table4.

                                      TABLE 4                                     __________________________________________________________________________                    Amount of                                                                           Compressive                                                                          Abrasion                                                                           Amount of                                                   filler used                                                                         strength                                                                             loss water sorption                              Monomer composition                                                                           (α-SiO.sub.2)                                                                 (kg/cm.sup.2)                                                                        (cm.sup.3)                                                                         (mg/cm.sup.2)                               __________________________________________________________________________    1 TMM-3A(55)/TMM-4A(45)                                                                       82 wt %                                                                             2,850  0.43 0.28                                        2 TMM-3M(55)/TMM-4M(45)                                                                       "     2,870  0.40 0.29                                        __________________________________________________________________________

It follows from the above table that if TMM-3M (55)/TMM-4M(45) is to besubstituted for TMM-3A(55)/TMM-4A(45) as the composite resin-formingmonomer, the dental material obtained will have equally excellentphysical properties in the compressive strength, abrasion loss andamount of water sorption. That is, it is noted there that not onlytetramethylolmethane tri- or tetra-acrylate, but alsotetramethylolmethane tri- or tetra-methacrylate should be preferred asthe composite resin-forming monomer of the present invention.

EXAMPLE 5

Using, as the composite resin-forming monomer, mixed monomers comprisinga combination of TMM-3A and TMM-4A belonging to the present inventionand conventionally known dental resin-forming monomers Paste A 5-1, B5-1 and Paste A 5-2 and B 5-2 were prepared. Following the sameprocedure as that of Example 1 these pastes were mixed for thepreparation of composite resins.

    ______________________________________                                                             Part by weight                                           ______________________________________                                        Paste A 5-1                                                                   TMM-3A                 50                                                     TMM-4A                 30                                                     Bis-MEPP               13                                                     NPGDMA                 7                                                      N,N'--bis(2-hydroxyethyl)-4-dimethylaniline                                                          1.0                                                    Silane treated α-SiO.sub.2                                                                     456                                                    Paste B 5-1                                                                   TMM-3A                 50                                                     TMM-4A                 30                                                     Bis-MEPP               13                                                     NPGDMA                 7                                                      Silane treated α-SiO.sub.2                                                                     456                                                    Benzoyl peroxide       1.2                                                    Paste A 5-2                                                                   TMM-4A                 80                                                     Bis-GMA                10                                                     NPGDMA                 10                                                     N,N--bis(2-hydroxyethyl)-4-methylaniline                                                             0.8                                                    Silane treated α-SiO.sub.2                                                                     456                                                    Paste B 5-2                                                                   TMM-4A                 80                                                     Bis-GMA                10                                                     NPGDMA                 10                                                     Benzoyl peroxide       1.0                                                    Silane treated Si.sub.3 N.sub.4                                                                      456                                                    ______________________________________                                    

Compressive strength and abrasion loss were measured of these curedcomposite resins and results were tabulated in Table 5.

                  TABLE 5                                                         ______________________________________                                                                    Compres- Abra-                                                      Amount of sive     sion                                                       filler used                                                                             strength loss                                     Monomer composition                                                                             (α-SiO.sub.2)                                                                     (kg/cm.sup.2)                                                                          (cm.sup.3)                               ______________________________________                                        1   TMM-3A(50)/TMM-4A(30)/                                                                          82 wt %   2,860  0.43                                       Bis-MEPP(13)/NPG(7)                                                       2   TMM-4A(80)/Bis-GMA(10)/                                                                         "         2,840  0.41                                       NPG(10)                                                                   ______________________________________                                    

It is noticed from the above table that the cured composite resins usingmixed monomers prepared by mixing about 20% by weight of conventionallyknown dental resin-forming monomers, such as Bis-MEPP, NPG, Bis-GMA andso on, to the composite resin-forming monomer belonging to the presentinvention should also be valuable as dental material in terms of theirphysical property values. They did not give rise to any compatibilityproblem.

EXAMPLE 6

Following the procedure for the preparation of filler in section (1)-1there were prepared various silane-treated inorganic fillers asmentioned in the following Table 6. Then, using, as the compositeresin-forming monomer, mixed monomers prepared by mixing conventionallyknown bisphenol A diglycidyl methacrylate (bis-GMA) andtriethyleneglycol dimethacrylate (TEG) in proportions of 80:20 (byweight ratio), silane-treated inorganic filler, catalyst and activator,Paste A-6 and Paste B-6 of following compositions were preparedfollowing the procedure for the preparation of monomer paste in section(1)-2.

Paste A-6 and Paste B-6 were taken each in equal amounts, mixed andkneaded together on kneading paper at room temperature for 30 secondsfor the preparation of composite resins.

This composite resin was loaded in a stainless steel pipe with innerdiameter of 10 mm and height of 5 mm at one end and excess part wasremoved off with sheeted glass. Then, an injection needle was stuck intothe surface of the composite resin at intervals of 10 seconds at roomtemperature to determine the curing time. It was about 3 minutes long.

The filler used was of powder form with particle size of 50 microns orless. Paste A was incorporated withN,N-bis-(2-hydroxyethyl)-4-methylaniline as the polymerization activatorand Paste B was incorporated with benzoyl peroxide as the catalyst and2,5-di-tert, butyl-4-methylphenyl (BHT) as the polymerization inhibitor.

    ______________________________________                                                            Part by weight                                            ______________________________________                                        Paste A                                                                       Bis-GMA(80)/TEGDMA(20)                                                                              100                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                           2                                                       Silane treated inorganic filler                                                                     400                                                     Paste B                                                                       Bis-GMA(80)/TEGMA(20) 100                                                     Benzoyl peroxide      2.5                                                     BHT                   0.25                                                    Silane treated inorganic filler                                                                     400                                                     ______________________________________                                    

Compressive strength and abrasion loss were measured of this curedcomposite resin. Results were tabulated in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                  Filler            Compressive                                                                          Abrasion                                                         Amount*.sup.2                                                                       strength                                                                             loss                                   Monomer composition*.sup.1                                                                  Kind                                                                              Mohs' hardness                                                                        (wt %)                                                                              (kg/cm.sup.2)                                                                        (cm.sup.3)                             __________________________________________________________________________    1 Bis-GMA(80)/TEG(20)                                                                       Si.sub.3 N.sub.4                                                                  9<      80    2,750  0.27                                   2 "           AlN 7-8     "     2,570  0.33                                   3 "           BN  9<      "     2,800  0.26                                   4 "           VN  9       "     2,660  0.28                                   5*                                                                              "           α-SiO.sub.2                                                                 7       "     2,260  0.60                                   6*                                                                              "           Al.sub.2 O.sub.3                                                                  9       "     2,260  0.56                                   __________________________________________________________________________     *indicates Control.                                                           Note                                                                          *.sup.1 In the case of mixed monomer parentheses () following upon a shor     form for each monomer indicates a weight ratio of the monomer.                *.sup.2 the amount of filler used indicates a weight percentage of filler     based on the total amount of the monomer and the filler.                 

It follows from the above table that the composite resins (Run Nos. 5and 6) comprising a combination of Bis-GMA/TEG conventionally known asthe composite resin-forming monomer for medical or dental use andpowdered alumina filler having exceptionally high hardness and abrasionresistance among conventionally known fillers (with a Mohs' scale ofhardness of 9) or most widely used α-SiO₂ are still far fromsatisfactory in the compressive strength and abrasion resistance, butthe composite resins (Run Nos. 1-4) in combination with the filler whichis comprised of metal nitride belonging to the present invention andwhich is 7 or more in the Mohs' scale of hardness have markedly highcompressive strength and abrasion resistance.

EXAMPLE 7

Pastes of following compositions were prepared using, as the compositeresin-forming monomer, conventionally knownbismethacryloxyethoxyphenylpropane (Bis-MEPP), neopentylglycoldimethacrylate (NPG) and trimethylolpropane triacrylate (TMPT) and asthe filler, conventionally most widely used α-SiO₂ or Si₃ N₄ belongingto the present invention. Following the same procedure as that ofExample 6 these pastes were mixed and kneaded together for thepreparation of composite resins.

    ______________________________________                                                            Part by weight                                            ______________________________________                                        Paste A 7-1                                                                   Silane treated filler 400                                                     Bis-MEPP              100                                                     N,N--bis(2-hydroxyethyl-4-methylaniline                                                             1.0                                                     Paste B 7-1                                                                   Silane treated filler 400                                                     Bis-MEPP              100                                                     Benzoyl peroxide      2.0                                                     BHT                   0.15                                                    Paste A 7-2                                                                   Silane treated filler 400                                                     NPGDMA                100                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                           2.0                                                     Silane treated filler 400                                                     NPGDMA                100                                                     Benzoyl peroxide      2.5                                                     BHT                   0.10                                                    Paste A 7-3                                                                   silane treated inorganic filler                                                                     400                                                     TMPT                  100                                                     N,N--bis-(2-hydroxylethyl)-4-methylaniline                                                          1.5                                                     Paste B 7-3                                                                   Silane treated inorganic filler                                                                     400                                                     TMPT                  100                                                     Benzoyl peroxide      2.5                                                     BHT                   0.15                                                    ______________________________________                                    

Compressive strength and abrasion loss were measured of these curedcomposite resins. Results were tabulated in Table 7.

                  TABLE 7                                                         ______________________________________                                                Filler      Compressive                                                                              Abrasion                                                         Amount    strength loss                                     Monomer   Kind    (wt %)    (kg/cm.sup.2)                                                                          (cm.sup.3)                               ______________________________________                                        1 Bis-MEPP                                                                              Si.sub.3 N.sub.4                                                                      80        2,890    0.24                                     2 NPGDMA  "       "         2,930    0.25                                     3 TMPT    "       "         3,000    0.23                                     4* Bis-MEPP                                                                             α-SiO.sub.2                                                                     "         2,410    0.58                                     5* NPGDMA "       "         2,450    0.57                                     6* TMPT   "       "         2,470    0.57                                     ______________________________________                                    

The above table shows that in comparison with composite resins (Run Nos.4-6) comprising a combination of Bis-MEPP, NPGDMA or TMPT conventionallyknown as the composite resin-forming monomer for medical or dental useand conventionally known filler α-SiO₂, the composite resins (Run Nos.1-3) comprising a combination of these conventionally known monomers andSi₃ N₄, the filler belonging to the present invention, should have muchhigher compressive strength and abrasion resistance.

EXAMPLE 8

Using, as the composite resin-forming monomer, mixed monomer prepared bymixing TMM-3A and TMM-4A belonging to the present invention inproportions of 55:45 (by weight ratio) and as the powdery filler,conventionally known metal oxide or metal nitride belonging to thepresent invention in such given amounts as indicated in the followingTable 8 Paste A 8 and Parts B 8 of following compositions were prepared.

    ______________________________________                                                            Part by weight                                            ______________________________________                                        Paste A 8                                                                     Various powdery fillers                                                                             in given amounts                                                              as indicated                                                                  in Table 8                                              TMM-3A(55)/TMM-4A(45) 100                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                           2                                                       Paste B 8                                                                     Various powdery fillers                                                                             in given amounts                                                              as indicated in                                                               in Table 8                                              TMM-3A(55)/TMM-4A(45) 100                                                     Benzoyl peroxide      2.5                                                     BHT                   0.15                                                    ______________________________________                                    

Compressive strength and abrasion loss were measured of these curedcomposite resins. Results were tabulated in Table 8.

                                      TABLE 8                                     __________________________________________________________________________                     Filler           Compressive                                                                          Abrasion                                                          Amount                                                                             strength                                                                             loss                                 Monomer composition                                                                            Kind                                                                              Mohs' hardness                                                                        (wt %)                                                                             (kg/cm.sup.2)                                                                        (cm.sup.3)                           __________________________________________________________________________    1  TMM-3A(55)/TMM-4A(45)                                                                       Si.sub.3 N.sub.4                                                                   9<     75   3,080  0.22                                 2  "             α-SiO.sub.2                                                                 7       "    2,570  0.49                                 3  "             Al.sub.2 O.sub.3                                                                  9       "    2,570  0.47                                 4  "             Si.sub.3 N.sub.4                                                                   9<     80   3,200  0.19                                 5  "             AlN 7-8     "    2,980  0.25                                 6  "             ZrN 8-9     "    3,010  0.23                                 7  "             NbN 8       "    2,860  0.25                                 8  "             TiN 8-9     "    3,020  0.24                                 9  "             BN   9<     "    3,280  0.16                                 10 "             BN  9       "    3,140  0.20                                 11 "             α-SiO.sub.2                                                                 7       "    1,720  0.46                                 12 "             Al.sub.2 O.sub.3                                                                  9       "    2,720  0.45                                 __________________________________________________________________________

It follows from the above table that when making comparisons ofcompressive strength and abrasion loss between the cured compositeresins (Run Nos. 2, 3, 11 and 12) prepared by combining α-SiO₂ or Al₂O₃, being conventionally known filler, with TMM-3A(55)/TMM-4A(45), beingthe monomer of the present invention, and the cured composite resins(Run Nos. 1, 4-10) in combination with the metal nitride with a Mohs'scale of hardness of 7 or more, the filler of the present invention, thelatter ones should be better in the compressive strength and abrasionloss.

It is also noted there that with the cured composite resins using, asthe filler, the metal nitride belonging to the present invention BN, VNand SI₃ N₄ with a Mohs' scale of hardness of 9 or more showexceptionally high compressive strength and abrasion resistance and thatthey should be suited to use as crown bridge restoratives or fillingmaterials in molars.

It also follows from comparisons between Run Nos. 1 and 4, between RunNos. 2 and 11 and between Run Nos. 3 and 12 that the compressivestrength and abrasion resistance both are enhanced in proportions to theamount of filler used.

EXAMPLE 9

Composite resins were prepared following the same procedure as that ofExample 6 except that there were used, as the composite resin-formingmonomer, TMM-3A (55)/TMM-4A(45) belonging to the present invention,conventionally known Bis-GMA(80)/TEGDMA(20) andTMM-3A(44)/TMM-4A(36)/Bis-MEPP(20), as the powdery filler, those fillersmentioned in the following Table 9 in given amounts and further, theactivator and the catalyst each in given amounts mentioned in the Table9. Compressive strength and abrasion loss were measured of these curedcomposite resins. Results were tabulated in Table 9.

                                      TABLE 9                                     __________________________________________________________________________                                    Amount of                                                                           Amount of                                                               activator                                                                           catalyst                                                       Filler   (part/200                                                                           (part/200                                                                           Compressive                                                                          Abrasion                                              Amount                                                                             parts of                                                                            parts of                                                                            strength                                                                             loss                       Monomer composition    Kind                                                                              (wt %)                                                                             monomer)                                                                            monomer)                                                                            (kg/cm.sup.2)                                                                        (cm.sup.3)                 __________________________________________________________________________    1 TMM-3A(55)/TMM-4A(45)                                                                              SiN.sub.4                                                                         85   2.0   2.5   3,350  0.16                       2   "                  "   90   "     "     3,520  0.14                       3   "                  ZrN 80   "     "     3,010  0.23                       4   "                  TiN "    "     "     3,020  0.24                       5 TMM-3A(44)/TMM-4A(36)/Bis-MEPP(20)                                                                 SiN.sub.4                                                                         "    1.0   2.0   3,220  0.17                       6*                                                                              Bis-GMA(80)/TEG(20)  α-SiO.sub.2                                                                 "    2.0   2.5   2,260  0.60                       __________________________________________________________________________     *BHT was used in the amount of 0.15 (part/200 parts of monomer) in Run        Nos. 1-5 and in the amount of 0.25 (part/200 parts of monomer) in Run No.     6.                                                                       

In the comparisons of the in compressive strength as well as theabrasion loss with the cured composite resin (Run No. 6) with acombination of conventionally known monomer Bis-GMA(80)/TEG(20) andknown filler α-SiO₂ a first glance at the above table shows that bymaking the composite resin-forming material by combining the monomercontaining 80% or more of TMM-3A(55)/TMM-4A(45), the monomer of thepresent invention, with SiN₄, ZrN or TiN, the metal nitride, thecomposite resin formed should have specifically excellent compressivestrength and abrasion resistance.

When comparing the amounts in which the filler can be combined with thecomposite resin-forming monomer in such a range as not to give rise tothe operation problem of the composite resin paste, the monomercontaining 80% or more of TMM-3A(55)/TMM-4A(45), the monomer of thepresent invention, could be incorporated with the filler in greateramounts than the Bis-GMA(80)/TEG(20). This is conceived to be attributedto the difference in the fluid characteristics of the monomer. As isclear from a comparison between Run No. 1 and Run No. 2, because ofcompressive strength and abrasion resistance increase in proportion tothe amount of filler used, obviously the composite resin having a highercompressive strength and abrasion resistance could be obtained whenusing, as the composite resin-forming material, the monomer of thepresent invention capable of incorporating a great deal of fillerwithout causing trouble in the operation.

EXAMPLE 10

Composite resins were prepared following the same procedure as that ofExample 6, using, as the composite resin-forming monomer,TMM-3A(55)/TMM-4A(45) or Bis-GMA(80)/TEGDMA(20) and as the powderyfiller, single compounds or mixtures of various fillers mentioned below.

The following are compositions of the respective pastes used in thepreparation of composite resins.

    __________________________________________________________________________                         Part by weight         Part by weight                    __________________________________________________________________________    Paste A 10-1                 Paste B 10-1                                     TMM-3A(55)/TMM-4A(45)                                                                              100     TMM-3A(55)/TMM-4A(45)                                                                        100                               Si.sub.3 N.sub.4     400     α-SiO.sub.2                                                                            400                               N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                          2       Benzoyl peroxide                                                                             2.5                                                            BHT            0.15                              Paste A 10-2                 Paste B 10-2                                     TMM-3A(55)/TMM-4A(45)                                                                              100     TMM-3A(55)/TMM-4A(45)                                                                        100                               Si.sub.3 N.sub.4     400     Al.sub.2 O.sub.3                                                                             400                               N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                          2       Benzoyl peroxide                                                                             2.5                                                            BHT            0.15                              Paste A 10-3                 Paste B 10-3                                     TMM-3A(55)/TMM-4A(45)                                                                              100     TMM-3A(55)/TMM-4A(45)                                                                        100                               Si.sub.3 N.sub.4     400     Si.sub.3 N.sub.4                                                                             400                               N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                          2       Benzoyl peroxide                                                                             2.5                                                            BHT            0.15                              Paste A 10-4                 Paste B 10-4                                     Bis-GMA(80)/TEGDMA(20)                                                                             100     Bis-GMA(80)/TEGDMA(20)                                                                       100                               Si.sub.3 N.sub.4     400     α-SiO.sub.2                                                                            400                               N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                          2       Benzoyl peroxide                                                                             2.5                                                            BHT            0.25                              Paste A 10-5                 Paste B 10-5                                     Bis-GMA(80)/TEGDMA(20)                                                                             100     Bis-GMA(80)/TEGDMA(20)                                                                       100                               α-SiO.sub.2    400     α-SiO.sub.2                                                                            400                               N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                          2       Benzoyl peroxide                                                                             2.5                                                            BHT            0.25                              __________________________________________________________________________

                  TABLE 10                                                        ______________________________________                                                  Filler     Compressive                                                                              Abrasion                                      Monomer             Amount   strength loss                                    composition Kind    (wt %)   (kg/cm.sup.2)                                                                          (cm.sup.3)                              ______________________________________                                        1   TMM-3A(55)/ Si.sub.3 N.sub.4                                                                      40     2,960    0.33                                      TMM-4A(45)  α-SiO.sub.2                                                                     40                                                    2   TMM-3A(55)/ Si.sub.3 N.sub.4                                                                      40     2,975    0.32                                      TMM-4A(45)  Al.sub.2 O.sub.3                                                                      40                                                    3   TMM-3A(55)/ Si.sub.3 N.sub.4                                                                      80     3,200    0.19                                      TMM-4A(45)                                                                4   Bis-GMA(80)/                                                                              Si.sub.3 N.sub.4                                                                      40     2,505    0.44                                      TEGDMA(20)  α-SiO.sub.2                                                                     40                                                    5*  Bis-GMA(80)/                                                                              α-SiO.sub.2                                                                     80     2,260    0.60                                      TEGDMA(20)                                                                ______________________________________                                    

It is noted from the above table that in comparison of the compositeresin (Run No. 5) with a combination of Bis-GMA(80)/TEGDMA(20), theconventionally known composite resin (Run No. 4) comprising the saidmonomer and the known filler α-SiO₂ of which one half the amount wasreplaced by Si₃ N₄, the filler of the present invention, with the curedcomposite resin formed by use of only a small amount of the filler ofthe present invention the filler is very great in the extent to which itcontributes to the improvements of the compressive strength and abrasionresistance.

It is also noted from a comparison between Run No. 4 and Run No. 1 thatthe monomer of the present invention should bring about a greater effectof the improvement of the compressive strength and abrasion resistance.

It follows from a comparison between Run No. 5 and Run No. 3 that if themonomer of the present invention and the filler of the present inventionare to be substituted for the known monomer and the known filler, thecompressive strength and abrasion resistance will be much more improved.

Furthermore, as the result of testing the stability of these pastes forthe preparation of composite resins, those prepared by incorporating themetal nitride of the present invention into Paste B went more or lessbad in the storage stability as compared to those in whichconventionally known α-SiO₂ or Al₂ O₃ was incorporated. Even if suchcases, it is noted that by using the metal nitride of the presentinvention as the filler for Paste A and conventionally known filler,such as α-SiO₂ and so on, as the filler for Paste B and combiningtogether these both pastes the cured composite resin obtained will bestabilized in storage and markedly excellent in mechanicalcharacteristics.

EXAMPLE 11

TMM-3A/TMM-4A, the typical example of the present invention, andconventionally known Bis-GMA/TEG, as the composite resin-forming monomerand Si₃ N₄ of the present invention, and conventionally known α-SiO₂, asthe filler were chosen and these monomers and fillers were combinedtogether for the preparation of 4 types each of pastes--Parts A 11-1 toA 11-4 and Paste B 11-1 to B 11-4--were prepared.

    ______________________________________                                                             Part by weight                                           ______________________________________                                        Paste A 11-1                                                                  TMM-3A                 55                                                     TMM-4A                 45                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                            0.6                                                    Silane treated Si.sub.3 N.sub.4                                                                      400                                                    Paste B 11-1                                                                  TMM-3A                 55                                                     TMM-4A                 45                                                     Benzoyl peroxide       0.8                                                    Silane treated Si.sub.3 N.sub.4                                                                      400                                                    Paste A 11-2                                                                  TMM-3A                 55                                                     TMM-4A                 45                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                            0.6                                                    Silane treated α-SiO.sub.2                                                                     400                                                    Paste B 11-2                                                                  TMM-3A                 55                                                     TMM-4A                 45                                                     Benzoyl peroxide       0.8                                                    Silane treated α-SiO.sub.2                                                                     400                                                    Paste A 11-3                                                                  Bis-GMA                80                                                     TEGDMA                 20                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                            0.6                                                    Silane treated Si.sub.3 N.sub.4                                                                      400                                                    Paste B 11-3                                                                  Bis-GMA                80                                                     TEGDMA                 20                                                     Benzoyl peroxide       0.8                                                    Silane treated Si.sub.3 N.sub.4                                                                      400                                                    Paste A 11-4                                                                  Bis-GMA                80                                                     TEGDMA                 20                                                     N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                            0.6                                                    Silane treated α-SiO.sub.2                                                                     400                                                    Paste B 11-4                                                                  Bis-GMA                80                                                     TEGDMA                 20                                                     Benzoyl peroxide       0.8                                                    Silane treated α-SiO.sub.2                                                                     400                                                    ______________________________________                                    

Compressive strength, abrasion loss, toothbrush abrasion loss, amount ofwater sorption, linear thermal expansion coefficient, Knoop hardness,tensile strength, coloring property and bonding strength were measuredof these various cured composite resins. Results were tabulated in Table11(1) and Table 11(2).

                                      TABLE 11(1)                                 __________________________________________________________________________                                         Toothbrush                                                                          Amount of                                                                           Linear thermal                               Filler   Compressive                                                                          Abrasion                                                                           abrasion                                                                            water expansion                                        Amount                                                                             strength                                                                             loss loss  sorption                                                                            coefficient                  Monomer composition                                                                           Kind                                                                              (wt %)                                                                             (kg/cm.sup.2)                                                                        (cm.sup.3)                                                                         (wt %)                                                                              (mg/cm.sup.2)                                                                       (× 10.sup.-6                                                            /°C.)                 __________________________________________________________________________    1 TMM-3A(55)/TMM-4A(45)                                                                       Si.sub.3 N.sub.4                                                                  80   3,200  0.19 0.054 0.30  20.5                         SiO.sub.2       α                                                         "             2,780                                                                             0.40 0.100  0.28 26.5                                     3 Bis-GMA(80)/TEG(20)                                                                         Si.sub.3 N.sub.4                                                                  "    2,530  0.31 0.120 0.42  26.1                         4*                                                                            SiO.sub.2       α                                                         "             2,260                                                                             0.60 0.215  0.42 30.0                                     __________________________________________________________________________     *indicates Control.                                                      

                                      TABLE 11(2)                                 __________________________________________________________________________                                    Coloring property                                                                       Bonding strength                                 Filler        Tensile                                                                            (ΔE)                                                                              (kg/cm.sup.2)                                        Amount                                                                             Knoop                                                                              strength  Un-  Bovine enamel                                                                          Bovine                     Monomer composition                                                                        Kind                                                                              (wt %)                                                                             hardness                                                                           (kg/cm.sup.2)                                                                      Polished                                                                           polished                                                                           (1) (2)  dentin                     __________________________________________________________________________    1 TMM-3A(55)/                                                                              Si.sub.3 N.sub.4                                                                  80   81   490  2.68 4.73 60-70                                                                             --   10-15                        TMM-4A(45)                                                                  2 TMM-3A(55)/                                                                              α-SiO.sub.2                                                                 "    70   470  2.21 4.92 60-70                                                                             100-105                                                                            10-15                        TMM-4A(45)                                                                  3 Bis-GMA(80)/                                                                             Si.sub.3 N.sub.4                                                                  "    74   410  2.35 4.90 30-40                                                                             --   0-5                          TEG(20)                                                                     4*                                                                              Bis-GMA(80)/                                                                             α-SiO.sub.2                                                                 "    54   360  3.88 10.23                                                                              30-40                                                                             --   0-5                          TEG(20)                                                                     __________________________________________________________________________     *indicates Control.                                                      

It follows from the above Table that the composite resins belonging tothe present invention (Run Nos. 1-3), as compared to the composite resin(Run No. 4) prepared by combining together the conventionally knowncomposite resin-forming monomer and filler, have such characteristicfeatures as to be less in the linear thermal expansion coefficient aswell as in the amount of water sorption, toothbrush abrasion loss anddiscoloration or the like, besides markedly excellent mechanicalstrengths, such as compressive strength, abrasion resistance, Knoophardness, tensile strength and so on, and markedly excellent bonding tothe hard tissue of the human body, and can be advantageously used asmedical or dental material. These excellent properties of the compositeresins of the present invention are particularly marked in the compositeresin (Run No. 1) with a combination of the monomer of the presentinvention and the filler of the present invention and these compositeresins are applicable to molars requiring markedly high mechanicalstrengths.

In the column of bonding strength to the bovine enamel in the abovetable, (1) indicates bonding strength when applying the composite resinas such to the bovine enamel and (2) indicates the bonding strength whencoating the bovine enamel surface with a mixture of equal amounts ofbonding agents A and B of following compositions found anew by theinstant inventors and set forth in another co-pending Patent Applicationfiled claiming the priority based on Japanese Patent Application No.54-44751, followed by application of the composite resin. It is notedfrom a comparison of bonding strengths to the bovine enamel in (1) and(2) of Run No. 2 that it is very effective in the point of bondabilityif the composite resin is applied after precoating the hard tissue ofthe human body with the said bonding agent.

    ______________________________________                                                             Part by weight                                           ______________________________________                                        Bonding agent A                                                               TMM-3A                 98                                                     Tetraisopropyltitanate 2                                                      N,N--bis-(2-hydroxyethyl)-4-methylaniline                                                            2                                                      Bonding agent B                                                               TMM-3A                 98                                                     Tetraisopropyltitanate 2                                                      Benzoyl peroxide       2                                                      2,5-di-tert. butyl-4-methylphenol                                                                    0.15                                                   ______________________________________                                    

EXAMPLE 12

Paste A 11-1 and Paste B 11-1 and Paste A 11-2 and Paste B 11-2mentioned in Example 11 were mixed respectively in equal amounts for thepreparation of composite resins of Run Nos. 1 and 2 in the followingTable 12. By using them cytotoxicity tests by tissue culture wereconducted.

The composite resin was enclosed in a glass tube with a surface area of28.3 mm², the specimen immediately after curing was immersed in 5 ml ofculture medium (199) and rotated at a rate of 200 r.p.m. at 37° C. for24 hours and then 1 ml of the medium was interacted with L-cells(2.8×10⁴) to count cell numbers after 2 days and after 4 days. Resultswere shown in Table 12.

Likewise, cytotoxity tests were conducted on the composite resincomprising Paste A 1-2 and Paste B 1-2 of Example 1 and results werealso tabulated in Table 12.

                  TABLE 12                                                        ______________________________________                                                               Cell numbers                                                       Filler     in 1 ml                                                Monomer               Amount   After  After                                   composition   Kind    (wt %)   2 days 4 days                                  ______________________________________                                        Blank   --        --      --     4.6 × 10.sup.4                                                                 56 × 10.sup.4                   1     TMM-3A(55)/ Si.sub.3 N.sub.4                                                                      80     3.0 × 10.sup.4                                                                 24 × 10.sup.4                         TMM-4A(45)                                                              2     TMM-3A(55)/ α-SiO.sub.2                                                                     "      3.2 × 10.sup.4                                                                 22 × 10.sup.4                         TMM-4A(45)                                                               3*   Bis-GMA(80)/                                                                              α-SiO.sub.2                                                                     75     2.3 × 10.sup.4                                                                 19 × 10.sup.4                         TEGDMA(20)                                                              ______________________________________                                         *indicates Control.                                                      

As clear from the above table, the composite resin of the presentinvention is less in the action of inhibiting the cell multiplication ascompared to the conventional type of composite resin.

EXAMPLE 13

Clinical observations were conducted by the following procedure. Cariesof a patient was removed by a dental drill and it was cleansed withwater and the enamel of the caries was immediately coated by a brushwith 40% phasphate etching solution. After one minute it was cleansedwith water and further dried in an air stream for the formation of aclean enamel surface.

Then, the enamel surface in the cavity including this surface was thinlycoated by sponge cotton with a mixture of equal amounts of bondingagents A and B mentioned in Example 11. Respectively different compositeresins were applied to the caries in molars and in anterior teeth. Thatis, the composite resin prepared by mixing Paste A 11-1 and Paste B 11-1mentioned in Example 11 with powdered Si₃ N₄ incorporated as the fillerwas applied to molars, whereas the composite resin prepared by mixingPaste A 11-2 and Paste B 11-2 mentioned in Example 11 with powderedα-SiO₂ incorporated as the filler was applied to anterior teeth. Thecomposite resin prepared by mixing and kneading together these Paste Aand Paste B in equal amounts was immediately enclosed in the cavity andsimultaneously, the filled portion was pressed and held on withcelluloid strips for 5 minutes whereby the composite resin was cured.After it was cured, the celluloid strips were removed, the form was putin order by the dental drill and treatment was finished.

The following are results of these clinical observations.

(1) Results of application to molars:

Class 1 and Class 2 cavities in molars, in particular were filled. Therewere 106 clinical cases.

Conventionally molars were being filled with dental amalgamrestoratives, such as an amalgam of silver alloy and mercury. Variousproblems, however, were indicated of these dental amalgam restorativematerials, such as lacking bonding strength with the tooth, low in themarginal seal, toxicity and so on.

The composite resin of the present invention is nearly free of any suchdefects as seen in the dental amalgam restorative material. That is, ithas sufficient bonding strength to the tooth and is free from fracturesin filled marginal portions frequently occurring in the amalgamrestorative material and hence, hardly any incidence of recurrent cariesis observed.

The composite resin of the present invention had sufficient bondingforce to teeth and it is free from fractures in the filled marginalportion frequently occurring at the time of filling with the dentalamalgam and the incidence of recurrent caries arising therefrom washardly observed. Further, the composite resin of the present inventionhas excellent mechanical strengths, such as compressive strength,abrasion resistance, tensile strength and so on, in addition tosteadfast bonding to the tooth and because of this, it hardly fell outeven if enclosed in molars which were subjected to higher occlusalpressures than anterior teeth.

It follows from these clinical test results that the composite resinwith a combination of the composite resin-forming monomer belonging tothe present invention and the metal nitride powdery filler of thepresent invention can fully withstand practical use, even if it isapplied to molars and it is superior in performance to the widely useddental amalgam restoratives as the conventional molar restorativefilling material.

(2) Results of application to anterior teeth:

Class 3 and Class 5 cavities, in particular, were filled. There were 129clinical cases. Conventionally anterior teeth were being filled withdental composite resins. These existing dental composite resins,however, are weak in mechanical strength, such as compressive strength,abrasion resistance and so on, and low in bonding strength and hence,indications were made of various problems, such as incidence ofrecurrent caries on the contact surface between the restorative fillingmaterial and the tooth with the lapse of time after the filling,discoloration and surface abrasion arising from biting, brush polishingand so forth.

The composite resin of the present invention, even with the lapse of six(6) months' time after its filling, was almost free from such problemsas indicated of the existing dental composite resin. The composite resinof the present invention was free from recurrent caries in the interfacewith the tooth because of the resin having high bonding strength to thetooth and high abrasion resistance. Not only that, but hardly anydiscoloration was observed.

These results of clinical observations show that the composite resincomprising a combination of the composite resin-forming monomerbelonging to the present invention and the existing metal oxide powderyfiller should be markedly excellent in the performance when applying asthe anterior tooth restorative filling material as compared to theexisting dental composite resin.

We claim:
 1. A dental filling material, consisting essentially of:(A)from about 50 to about 95% by weight of finely divided, inorganic fillermaterial which is safe and effective for use in a dental filling in thehuman body, wherein at least 50% by weight of said filler material is atleast one nitride substance having a Moh's hardness of at least 7 and isselected from the group consisting of vanadium nitride, boron nitride,aluminum nitride, silicon nitride, titanium nitride and zirconiumnitride, and the balance of said filler material is one or moreinorganic dental filler substances which are different from said nitridesubstance, having a Moh's hardness of at least 5 and are useful as afiller for dental filling materials, and (B) from about 50 to about 5%by weight of polymerizable monomer component capable of polymerizing toform a binder resin for dental filling materials, said polymerizablemonomer component being selected from the group consisting of(1)monomers having the formula ##STR11## wherein R is hydrogen or methyl, Xis alkylidene and Y is oxyalkylene having from 2 to 5 carbon atoms, (2)monomers having the formula ##STR12## wherein R₁ is CH₃, CH₃ CH₂ or CH₃CH₂ CH₂, and R₂ is H or CH₃, (3) monomers having the formula ##STR13##wherein R₁ is hydrogen or methyl, R₂ is alkylene and R₃ is a divalenthydrocarbon group, (4) neopentylglycol dimethacrylate, (5)triethyleneglycol dimethacrylate, (6) bisphenol A diglycidylmethacrylate, and mixtures thereof.
 2. A dental filling materialaccording to claim 1, in which said nitride substance is vanadiumnitride, boron nitride, aluminum nitride or silicon nitride.
 3. A dentalfilling material according to claim 1 or claim 2, in which said nitridesubstance has a particle diameter of 50 microns or less.
 4. A dentalfilling material according to claim 1 or claim 2, in which said nitridesubstance has a Moh's hardness of at least
 9. 5. A dental fillingmaterial according to claim 1 or claim 2, in which said nitridesubstance is coated with a silicon-containing keying agent.
 6. A dentalfilling material according to claim 5, in which said silicon-containingkeying agent is a silicon-containing organic compound having at leastthree alkoxy groups.
 7. A dental filling material according to claim 5,in which said silicon-containing keying agent is a silicon-containingorganic compound having three alkoxy groups and one organic grouppossessing, as a terminal group, a mono-olefinic hydrocarbon radical, aprimary amino group or an epoxy group.
 8. A dental filling materialaccording to claim 5, in which said silicon-containing keying agent isα-methacryloxypropyltrimethoxysilane or vinyltriethoxysilane.
 9. Adental filling material according to claim 1, in the form of two pastes,one paste consisting essentially of a mixture of said nitride substance,said polymerizable monomer (B) and an activator for activatingpolymerization of (B), and the second paste consists essentially of amixture of said inorganic dental filler substance different from saidnitride substance, said polymerizable monomer (B) and a catalyst forcatalyzing polymerization of (B).